Tungsten arc lamp



Sept. 21 1926.

M. PIRANI TUNGSTEN ARC LAMP Filed Feb. 8. 1923 Invenbor: Mar-celloPir-ani,

His Attorney Patented Sept. 21, 1926.

UNITED STATES v 1,600,843 PATENT- OFFICE.

MABGELLO PIRAN I, OF WILMERSDORF, NEAR BERLIN, GERMANY ASSIGNOR TO GEN-ERAL ELECTRIC COMP NY. A CORPORATION OF NEW YORK.

runesrnn mac LAMP.

Application filed February 8, 1923, Serial Ro. 617,858, and in GermanyApril 1, 1922.

My invention relates to improvements in arc lamps.

Heretofore arc lamps of the above char-- acter have required specialstarting apparatus when used in connection with the usual commerciallighting circuits.

Among the objects of my invention are the following: to provide atungsten arc lamp which automatically starts with the line voltage ofthe ordinary commercial lighting circuit without the provision ofspecial starting apparatus; and to provide details in improvement forincreasing the efliciency and serviceability of such lamps.

The means for accomplishing this are hereinafter more fully set forthand claimed. Referring to the accompanying drawing, Fig. 1 shows thelamp in elevation; Fig. 2 shows the lamp in modified form, the drawingbeing made partially in sections. Referring to these figures more indetail, itwill be seen that the lamp constructed. as shown in Fig. 1 hasa glass globe orbulb a and a socket engaging terminal I). The lead inwires (I pass through the usual stand 0 into the bulb and are connectedwith the electrodes 6 which are provided at their ends with suit-ableterminals such as the tungsten ball terminals f between which the arcplays. *The space between the two balls may be in the neighborhood ofone eighth of an inch. This distance of course may be varied with thegas pressure used. This lamp is filled with a gas such as argon andcontains also a quantity of mercury g ina metallic form as indicated.The argon is supplied in the bulb at a pressure of about 1 to 10 mm. Thevapor pressure of the mercury is very small while the lamp is cold andthe effect of the argon or other rare gas predominates. Therefore, thearc can be formed at the ordinary line pressure without any specialstarting or voltage raising apparatus. If the arc. is set up in anatmosphere of low pressure a very energetic atomization action of theelectrodes takes place, and I propose to control this by the use ofmercury vapor. The mercury in the lamp is heated when the arc isestablished, and therefore the mercury vaporizes and acts as a check onthe atomizing action onthe electrode.

It will be understood that the temperature of the lamp may be controlledby anysuitable-means during the operation so as to maintain the mercuryvapor at the required pressure.

This may be done for example by restricting the dimensions of the bulbin which the mercury n contained. The mercury pressure may be in theneighborhood of one atmosphere. llhen the lamp is constructed as aboveindicated a corona discharge first appears when the lamp is connectedacross the usual lighting circuit and this is followed by the formationof the are which is set up between the tungsten terminals f through theargon or other rare gas. Now as the temperature rises, the mercury vaporpressure increases and serves as a check as described. It is found thatsatisfactory results are obtained when the temperature of the mercury isheld at about 200 degrees C. during the operation of the lamp. In thelamp circuit a resist arms is introduced in series with .the lamp.

Referring to the modified form of the lamp-shown in Fig. 2, it will beseen that this form also has the electrodes 6 and the ball terminals 7.However, the electrodes in this form of lamp are led through narrowtubes 71. to the lower ends to which the bulb a is connected. The leadin wires d of course pass through the upper ends of the glass tubes.These wires (1 are, as shown, connected in the usual manner to thesocket engaging terminals of the bulb.

During the operation of the lamp of course the mercury is heated and themercury vapor pressure rises and in the form of lamp shown in Fig. 2,this mercury vapor forces the argon or other gas into the narrow tubesit. Obviously, therefore, the rare gas and the mercury come into contactonly in the narrow tubes. As a result of the foregoing construction, thecurrent inlet points are protected from any harmful heat- ,ing effect,since only the mercury containing bulb a is kept hot. For the protectionof the bulb a, I also provide in the construction of Fig. 2 an outerbulb i which may be connected with the outer air by a suitable openingat k.

It is obvious that in a lamp of this character I may use a-number ofelectrodes and I may arrange the same in different ways. Also, someother metal may be substituted for mercury to supply the heavy vapor. It

.will be understood that in place of having two tubes h, as shown inFig. 2, I may have a single small tube in which both of the leads e arecontained. In any event, the

lower 0 ening of the tube h should be made as smal as possible, butlarge enough to permit any mercury vapor which condenses therein to fallback into the bulb a.

What I claim as new and desire to secure bv'Letters Patent of the UnitedStates, is,

U 1. An are lamp having an enclosing sealed bulb, electrodes andterminals therein, an atmosphere in the bulb of one of the rare gases ata sufliciently small pressure to permit the-formation of an are betweenthe terminals at a comparatively low voltage and mercury in the bulb forproviding a higher vapor pressure during the operation of the lam saidlamp having a second enclosing bul container.

2. An arc lamp having a sealed contaming bulb enclosing a light gas andalso enclosing means for generatin a heavy gas and a compartment intowhich the lighter gas may be retired by the heavy gas when the heavy gasis generated and the pressure of the heavy gas is suflicientlyincreased, said light gas adapted to enable the arc to be formed underlow voltage, the are constitutin the only means for initiating thegeneration of the heavy gas to increase the gas pressure within the bulband whereby the light intensity of the arc may be increase In Witnesswhereof, I have hereunto set my hand this 17th day of January, 1923.

MARCELLO PIRANI.

